1. Field of the Invention
The present invention relates to image processing apparatuses, and in particular to image processing apparatuses which employ frequency modulation (FM) techniques, such as error diffusion, to provide tone process.
2. Description of the Related Art
Conventionally, FM techniques, such as error diffusion, FM screening, are known in the field of image processing. They provide tone representation by modulating a frequency which drives a print head. According to the techniques, images have darker tones at higher-frequency portions and lighter tones at lower-frequency portions.
Also known as an image processing method is a dither method which uses a dither matrix to provide a pseudo tone representation.
In printing images after this image processes, smaller dots provided more densely can provide images of higher quality. In order to provide smaller dots, however, the resolution of the printer must be increased. When an ink-jet printer has its resolution increased, its output rate is decreased. When a laser beam printer has its resolution increased, the cost of its optical system and the like is increased.
When the dither method is employed, mechanical noises of printers disadvantageously affect image quality. Error diffusion generates a patterned noise (snake noise) in intermediate tones.
The present invention has been made to overcome the above disadvantages. The present invention contemplates an image processing apparatus capable of improving image quality without changing the resolution of the printer.
The present invention also contemplates an image processing apparatus providing for image quality hardly affected by mechanical noises from the printer.
The present invention also contemplates an image processing apparatus capable of reducing a patterned noise in intermediate tones.
To achieve the above objects, in an aspect of the present invention an image processing apparatus includes a first processing unit applying a tone process on input image data, and a second processing unit determining a size of a dot to be printed from the data of a plurality of pixels included in image data having been subjected to the tone process.
In another aspect of the present invention an image processing method includes the steps of: applying a tone process on input image data; and determining a size of a dot to be printed from data of a plurality of pixels included in image data having been subjected to the tone process.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.